Science Objectives for Everyone
Investigating the Structure of Paramagnetic Aggregates from Colloidal Emulsions - 2 (InSPACE-2) will obtain data on magnetorheological fluids (fluids that change properties in response to magnetic fields) that can be used to improve or develop new brake systems and robotics.

Science Results for Everyone
Magnetorheological fluids are colloids, or fine particles suspended in fluid, that can form solid-like gels when exposed to a steady, uniform magnetic field. This experiment observed two distinct particle growth processes: one where particle-rich and particle-poor regions form, and another where the structure suddenly collapses and particle columns form. Magnetic field strength and frequency determine which of these two processes occur, and in microgravity, the particular structures can be maintained as long as the magnetic forces are applied. The results suggest how manipulating magnetic fields may be used to harness colloidal suspensions to create unique materials and electro-mechanical devices.

The following content was provided by Eric M. Furst, Ph.D., and is maintained in a database by the ISS Program Science Office.

Experiment Details

OpNom:

Principal Investigator(s)
Eric M. Furst, Ph.D., University of Delaware, Newark, DE, United States

InSPACE-2 will study the fundamental behavior of magnetic colloidal fluids under the influence of various magnetic fields. Observations of the microscopic structures will yield a better understanding of the interplay of magnetic, surface and repulsion forces between structures in magnetorheological (MR) fluids.

These fluids are classified as smart materials which transition to a solid-like state by the formation and cross-linking of microstructures in the presence of a magnetic field. On Earth, these materials are used for vibration damping systems that can be turned on or off.

This technology has promise to improve the ability to design structures, such as bridges and buildings, to better withstand earthquake forces.

Description
The Investigating the Structure of Paramagnetic Aggregates from Colloidal Emulsion - 2 (InSPACE-2) investigation is a continuation of the InSPACE investigation, begun on ISS Expedition 6, providing new and improved samples for operation in the Microgravity Science Glovebox (MSG). Magnetorheological (MR) fluids are suspensions of paramagnetic particles that can quickly solidify when exposed to a magnetic field and return to their original liquid state when the magnetic field is removed. This solidification process produces useful viscoelastic properties that can be harnessed for a variety of mechanical devices from intricate robotic motions to strong braking and clutch mechanisms. Understanding how to precisely control these properties and states will enable the use of MR fluids as a working fluid in exploration robots to produce a range of articulated motions ranging from delicate (as if picking up an egg) to firm response, and proper encapsulation pressure around bone fractures. Current robotic technology depends on conventional mechanical components (gears, dashpots, and clutches) while MR fluid interfaces provide significantly faster response, strength, tenability, and physical flexibility, to enhance human and robotic movement and strength.

Gravitational effects in MR fluids are manifested as variations in particle concentration and phase separation due to particle sedimentation, directly impacting rheological (viscoelastic) properties and application performance. Long-duration microgravity time is needed to study the internal structural evolution in the MR fluids in the absence of these additional effects. InSPACE-2 will provide feasibility data on the gelation transition in MR fluids under steady magnetic fields and perform runs using new samples with an improved cell design for imaging the resulting large aggregate structures, based on the previous InSPACE data.

InSPACE-2 hardware consists of two new Helmholtz coil assemblies containing sealed vials of MR fluid and eight new vial assemblies that hold the test fluid. The new hardware will interface with the InSPACE hardware currently on ISS. InSPACE-2 data will significantly impact design of human robotic interfaces for exploration missions.

Space Applications
At the practical level, these fluids are used in electromechanical interfaces and devices in which the fluid is operationally exposed to similar fields which can affect their operation. Current commercial MR fluid products include tunable dampers and brakes, while future applications in robotics, clutches, and a host of vibration-control systems are envisioned.

Earth Applications
The study of MR fluids on Earth is difficult because the small magnetic particles remain suspended while the sediments (large particles) sink. The low-gravity environment that is provided on the ISS will eliminate the effects of sinking sedimentation. After the magnetic field is applied to a MR fluid, the microstructures form a rigid lattice that causes the suspension to stiffen. The rapid transformation of these fluids without the iron oxide grains clumping have many possible technological applications on Earth, especially for actuator-type devices. This technology has promise to improve the ability to design structures, such as bridges and buildings, to better avoid earthquake damage.

Operational Requirements
InSPACE-2 will be conducted inside the MSG work volume, and the hardware will be powered (120 vdc) via MSG. The experiment runs will be recorded by MSG's video system. Using the optics from InSPACE-1 already on ISS, InSPACE-2 will visually study new samples. An improved cell design over that used in InSPACE-1 will be used for better imaging of the resulting aggregate structures. The new cells are dimensionally very thin in one direction which reduces the optical thickness in that direction and thus provides better viewing. A new coil is also provided that allows the substitution of multiple samples in two orthogonal orientations for alternate views. InSPACE-2 will provide data on the performance of magnetorheological (MR) fluids in a microgravity environment, under steady and intermittent operation (pulsed fields). InSPACE-2 is not a fully automated payload. The crew will be responsible for in-orbit operations, such as sample changes and video tape changes.

Operational Protocols
The crew will set up InSPACE inside the MSG work volume and conduct the 27 experiment runs using the glove ports. They will change out the coils after nine experiments and replace video tapes as necessary.

InSPACE-2 was performed during Expeditions 16, 18, 19 and 20, and completed its initial set of 42 test runs in 2009. Magnetorheological fluids are colloidal suspensions which can form solid-like gels when they are exposed to a steady, uniform magnetic field. Unique gel structures such as colloid-rich cylindrical columns can form within the fluid and be maintained by changing the field strength to relieve any structural stress (Furst 2009). For the InSPACE-2 experiment, two distinct particle growth processes were observed: one where particle-rich and particle-poor regions form and become "trapped", and the other where the system-spanning structure suddenly collapses and particle columns form. These two processes are separated by a distinct boundary that depends on the magnetic field strength and magnetic frequency, and results demonstrate how energy barriers preventing colloidal phase transition can be overcome by changing the magnetic driving frequency and forces. As with other experimental studies of colloids in microgravity, the results of the InSPACE-2 experiments show that in these gel systems, gravity plays a dominant role and would slowly compress and deform the gel structures when similar experiments are performed on Earth, whereas in space these structures can be maintained as long as the magnetic forces are applied. Through better understanding of the stable and unstable phase behavior in the absence of gravitational stresses, these results demonstrate how colloidal suspensions may be harnessed in the creation of unique materials and electro-mechanical devices by manipulating the magnetic forces holding them intact (Swan et al. 2012).